It was transported to my house by four pearly-skinned warriors atop an elephant. It was shipped in two separate jars made of quartz; while not fully active until combined, each jar was still quite toxic.
Alkahest, the Universal Solvent. I bought it online.
It shares a place next to the Elixir of Eternal Life and Philosopher's Stone on the bookshelf of alchemical myth, several shelves above comparative parlor tricks like Lunargent (moon-silver) and Parthenogenic Life.
Alkahest, of course, is the substance that can dissolve anything. Made properly, it will effortlessly destroy its way through the container, the hand holding it, the floor, and the core of the earth, sizzling like an angry perfect sun, leaving only a deep, clean hole.
How do you contain it, you might ask? Old carbon paper, made for messy reproduction of text. Modern carbon paper won't do it, even if it's chemically identical. It must be authentically obsolete. I think the theory is that carbon paper is already empty of essence, so the alkahest can't affect it. I suspect punch-cards or 8-tracks would also do the trick.
That's all I have to say about it. I wrote an earlier, much longer essay about alkahest, but I forgot to wrap the words in carbon paper, and the whole entry just dissolved.